Ester base lubricant compositions



United States Patent 3,093,585 ESTER BASE LUBRHIANT COMPOSITIONS HansLow and William W. Reynolds, East Alton, Ill., and

Donald W. Schmulling, St. Louis, Mo., assignors to Shell Oil Company,New York, N.Y., a corporation of Delaware No Drawing. Filed June 6,1960, Ser. No. 33,952

Claims. (Cl. 25237.2)

This invention relates to a lubricant composition containing a superiorantioxidant combination. More particularly, the present inventionrelates to an additive combinatrion for ester base lubricantcompositions having excellent stabilizing eiiects at extremely highlubricating temperatures.

One of the greatest problems in lubricating at high temperatures is todevelop a composition which will not easily oxidize to form acidiccomponents which in turn cause harmful deposits or sludges in thecomposition. This problem is especially difiicult to overcome whendealing with high temperatures such as encountered in modern aircraftgas turbine engines and hydraulic systems Where hot areas in the rangeof from 350-750 F. are contacted by the lubricant.

It is an object of the present invention to provide improved estercompositions. It is a particular object of the invention to provideester compositions having reduced tendencies to form acidic oxidationproducts. It is a particular object of the invention to provide esterlubricants especially useful as gas turbine lubricants and hydraulicfluids.

Now, in accordance with the present invention, a superior lubricantcomposition is provided comprising an estertype base fiuid and oxidationstabilizing amounts of both an amine of the group consisting of certaintriazines and certain pyridylamines in combination with criticallylimited proportions of complexes of such classes of amines with coppersalts of fatty acids. In one aspect of the invention provision is madefor partially oxidizing the amines to be used in the formation of suchcopper salt complexes. The optimum mol ratio of the combination is from2 to 75 mols of total amine for each mol of copper.

The copper complexes which are formed between the amine and the coppersalt are believed to be of the square planar type. However, the precisestructure of the complexes has not been absolutely determined. Theyappear to exist in a ratio of about 2 mols of the amine for each mol ofthe copper salt. Part of the unexpected character of the presentinvention lies in the fact that copper is known to be a seriousaccelerator of oxidation. Consequently the present invention is basedupon the discovery that an optimum ratio exists wherein an excess offiree amine is present beyond the amount necessary for forming thecomplex for the copper salt and within which ratio a remarkablestabilization of the oxidation properties of the ester base lubricant isobserved.

The copper salts to be employed in the preparation of the subjectcomplexes are preferably those with the copper in the second oxidativestate (copper II), while the fatty acid radical may be derived from anyfatty acid having from 2-24 carbon atoms. These include the usual acidssuch as acetic, propionic, butyric, hexoic, octanoic, :dodecanoic,cap-ric, caprylic, caproic, stearic, oleic, linoleic, etc. It ispreferred that the acid be saturated and have from 2 to 12 carbon atomsper molecule.

The amines which are utilized in their free form and also in complexwith the copper salt are of two general categories. These may bereferred to as pyridylamines and triazines. The pyridylamines are thosehaving at least one pyridyl radical and preferably two and compriseunsubstituted pyridylamines as well as alkyl substituted, and thosepyridylamines having assiibstituent groups amino radicals, arylradicals, aminoaryls, aminoalkyls, and triazyl radicals. Table A, whichfollows, lists typical pyridylamines coming within the scope of thisinvention.

TABLE A Pyridylamines Monopyr-idylamines:

2-pyridylamine 3 pyridylamine Dipyridylaniines:

2,2'-dipyridylamine 2,3 -dipyridylamine 2,4'-dipvridylamine3,3'dipyridylamine 4,4'-dipyridylamine Alkylpyridylamines:

2,2-di(4-ethylpyridyl) amine 4,4'-di( Z-tert-butylpyridyl) amine2-pyridyl-2'- 4-isopropylpyridyl) amine Aminopyridyl amines 2-tolyl-24-a1ninopyridyl amine 2,2-'( 3 -N-ethylaminopyridyl) amineArylpyridylamines:

(Z'pyridyl 2'-benzyl) amine (4-pyridyl) (2'-phenyl) amine (Z-pyridyl i2'-naphthyl) amine (Z-pyridyl) (Z-triazyl) amine The triazines may beused as the sole amine in the composition or may be combined with thepyridylamines. Suitable types are those constituted by unsubstitutedtriamine, or more preferably the guanamines in addition tomonoarninotriazines, alkyl triazines, aryltriazines or triazinylamine.Table 13 which follows lists typical species suitable for this purpose.

TABLE B Triazines Guanarnines:

2,4-diamino-6benzyl-triazine 2,4-diamino-6-methyl triazine2,4-diamino-6-propyl triazine 2,4-diamino-triazine 1-N-ethyl-2,4-diaminotriazine l-N-phenyl-ZA-diamino triazine 2,3-di-(N-ethyl)-2,4-diaminotriazine 1 35-tri (N-methyl -2,4-diaminotriazine 2,4-diamino6-phenyl-triazine Monoamlno triazines:

2- (N-methylamino) -triazine Z-(N-phenylamino) -triazine2-amino-tm'azine Alkyl triazines:

2,4-diethyltriazine 2,4,6-trimethyl triazine 2-methyl-4,-6-diethyltriazine 2-methyl-4-amino triazine The copper salt complexes of theseamine types may be formed in situ or may be preformed before dispersalin the ester base lubricants. The complexes are immediately formed bycombining solutions such as alcohol solutions of the amine and coppersalt and evaporating to dryness. However, complexes appear to be just asefficiently" formed by combining the free amine and the copper salt inthe ester lubricant.

While the structure of the complex has not been finalized, it isbelieved to be represented in a specific instance as according to thefollowing diagram:

The formation of metal complex is an equilibrium reaction; therefore, anexcess of free amine appears to serve two principal purposes. First, itminimizes the amount of free soluble copper ion which would act as apro-oxidant and secondly it assures as large an amount of activeinhibitor as possible by displacing the equilibrium toward the product,namely, the complex. If excessive amounts of the copper compound arepresent, then the pro-oxidant effect of copper becomes predominant andcauses an acceleration rather than a retardation of oxidation. On theother hand, if excessive amounts of free amine are present (or notenough copper to form sufficient amounts of the complex, the activeinhibitor) then the oxidation inhibition is minimized since the freeamines do not appear to be very eifective inhibitors. Thus, it was foundby means of comparative testing that the maximum oxidation inhibitionwas obtained when the mol ratio of total amine to copper was betweenabout 2 and about 75, preferably be tween about and about 35.

The mixtures of free amines and copper complexes are found to beeffective in aliphatic esters which are used primarily for synthetichydraulic fluids and gas turbine lubricants as well as for otherassociated purposes. Broadly, the principal classes included within thisbroad class of aliphatic esters comprise esters formed betweendicarboxylic acids and monohydric alcohols; esters formed betweenneopentyl glycols and monohydric-alcohols; esters of pentaerythritol orits dimers with monohydric alcohols; and the so-called complex esterswhich constitute various'combinations of dibasic acids, glycols andalcohols or dibasic acids, glycols and nonobasic acids. Table C outlinesthe various alternative structures contemplated as complex esters" aswell as listing briefly typical starting materials for the formation ofsuch esters.

TABLE C Complex esters (By ester-forming components):

Alcohol-(dibasic acid-glycol)-monobasic acid R OOCR COOR -OOCR See UJS.2,575,195 Alcohol-dibasic acid-(glycol-dibasic acid) -alcohol 4 R OOCRCOO(R -OOR COO) R See US. 2,703,811 Monobasic acid-glycol-(dibasicacid-glycol) monobasic acid R COOR -(OOCR COO--R -OOCR See US. 2,575,196Monohydric alcohols:

Z-ethylbutyl alcohol 2-ethylhexyl alcohol Monobasic acids:

Caproic acids Pelargonic acid Capric acid Glycols:

Neopentyl glycol Ethylene glycol Propylene glycol Dibasic acids:

Sebacic acid Azelaic acid As diesters there may be used one or more ofthe compounds of the formula ROOC-Z-COOR wherein Z is an alkylene chainof four to eight carbon atoms and R is an alkyl group of four tofourteen carbon atoms, being the residue of an aliphatic monohydricalcohol from butyl to tetradecyl alcohols. Dicarboxylic acids whichprovide the above esters are adipic, pimelic, suberic, azelaic, andsebacic. The alcohols include butyl, isobutyl, or sec-butyl alcohols andthe various amyl, hexyl, octyl, nonyl, decyl, undecyl, dodecyl, andtetradecyl alcohols. The alcohols with branched hydrocarbon chainsprovide diesters with particularly desirable properties. Typical ofthese are isobutyl, 2-ethylbutyl, 2-ethylhexyl, l-rnethylhexyl,l-methylheptyl, 1-methyl-4-ethyloctyl, 2,2, 4-trimethylhexyl,2-isopropyl-3,3-dimethylbutyl, 1,4-dimethylbutyl, and1-isobutyl-4-ethyloctyl alcohols.

Ester Lubes bis Z-ethylhexyl) sebacate bis (isononyl) sebacate bisZ-ethylhexyl) adipate bis( 1-methylheptyl)azelate bis(2,2,4-trimethylhexyl) pimelate bis( 1,4-diethylhexyl) adipate bis(1,4-dimethyloctyl) adipate bis 2-ethylbutyl) suberate 2-ethylhexyl)(isononyl) sebacate l-methylhexyl) (2-ethylbutyl) sebacate The aliphaticpolyesters which may be utilized as the lubricating fluids arepreferably tetraesters, such as the pentaerythritol esters or the dimersor trimers of the same. Preferably, each radical contains from 4 to 18carbon atoms each and preferably from 6 to 14 carbon atoms each. Typicalspecies include pentaerythritol tetracaproate, dipentaerythritolhexavalerate, pentaerythritol tetraheptoate, pentaerythiritol dicaproatedivalerate, pentaerythritol tricaproate heptoate and mixtures thereof.It will be noted that the esters may be either mixed esters or mixturesof homo esters, the best rheological properties being obtained withmixed esters and with mixtures of esters. For use at elevatedtemperatures the dipentaerythritol esters are preferred due to theirgreater molecular weight and consequently higher boiling points.

The course of oxidation as indicated by the rate of oxygen absorption inthe composition of this invention indicates that the amine in complexform with the copper salt is oxidized prior to its assumingits intendedfunction of acting as an oxidation inhibitor. The oxidation of the aminemay take place prior to or subsequent to incorporation of the amine inthe ester base lubricant. Consequently, the invention will be understoodto include the use of not only the amines per sebut also their oxidationproducts as' well as the copper complexes of such oxidized products. Theexact nature of the oxidation product has not been elucidated; however,the fraction of the oxidized product found to be most active in theprevention of oxidation of the ester base lubricant has anitrogen-to-copper molar ratio in the order of about 20-30, while theless effective fractions of the oxidized product have nitrogen-to-coppermolar ratios in the order of 36.

Still further and unexpected reductions in oxidation of the ester baselubricant are obtained by the additional presence of certain phenoliccompounds, particularly alkylene bisphenols. Such compounds arepreferably those typified by the following structure:

METHYLENE BISPHENOLS The phenolic compounds may be modified by thepresence of alkyl radicals on one or both of the phenolic nuclei.Typical compounds are as follows:

4,4-methylenebis(2,6-ditertiary-butylphenol) 4,4-methylenebis (2-2*ethylhexyl) phenol) 2,2'-methylenebis(4-isopropylphenol) The datacontained in the working examples will illustrate the benefits obtainedby the use of such bisphenols in addition to the combination of thecopper complex and free amines as described hereinbefore. The followingexamples illustrate the use of this invention.

EXAMPLE I Preparation of a copper complex betw en copper octoate and atria zine.An alcoholic solution of copper (II) octoate was mixed with analcoholic solution of 2,4-diamino 6-phenyll,3,5-triazine(benzoguanamine). The green precipitate has a meltingpoint of 2l0-214 C. and an elemental analysis showing that it contains55.4 percent by weight of carbon, 7.42 percent hydrogen, 13.3 percentnitrogen and 14.0 percent copper. This agrees with the postulatedformula However, the experimentally determined molecular weight was 945,almost twice as much as the empirical formula and indicates thelikelihood of dimerization. This is more plausible since it enables thecopper (II) to form a square planar complex.

EXAMPLE II Preparation of a copper salt compl x with adipyridylamine.-Copper (II) acetate and 2,2dipyridylamine were mixed inan alcoholic solution and evaporated to dryness. Analysis of the productgave an empirical formula of (C H N -(Ou)(C H O Accordingly, onemolecule of copper (II) acetate forms a planar complex with twomolecules of the bidentate ligand dipyridylamine. The complex contains17.5 percent copper and 11 percent nitrogen.

EXAMPLE III Oxidation inhibition of a mix d pentaerythritol ester.-- Apentaerythritol ester of a mixture of fatty acids averaging C C perester linkage was modified with 0.025 mol of 2,2-dip-yridylamine (22DPA)and with other TAB LE 1 Oxidation Inhibitor, 0.025 M time, hours 022-DgA/Cu acetate comple N Cu, Fe, Ag, AL- 68 o Copper octoate None 16Metal washers.

It will be seen by reference to the above table that the unmodified basefluid oxidized to the arbitrary limit set in about 14 hours (thearbitrary limit is that time required for the absorption of 1.0millimole of oxygen per gram of base fluid). The table also shows thatthe use of a well-known antioxidant, phenothiazine, resulted inextending this oxidation time (OT) to 37 hours. A standard phenolicinhibitor was not as effective as the latter. It is significant to notethat 2,2'-di-pyridylamine had essentially no oxidation inhibitingeffect. Copper octoate also exhibits substantially no oxidationinhibiting activity when utilized in the absence of an amine of thepresent invention. However, it is significant to note that when amixture of 2,2'-dipyridylamine and the copper acetate complex are mixedin the same base lubricant highly effective oxidation inhibition isobtained. Similar formulations wherein the metal catalysts (metalwashers of copper, iron, silver and aluminum) are replaced by a solublecopper salt exhibit the same inhibitory effect in the severalcompositions tested.

An investigation of the effect of mol ratio of free amine to coppercomplex was made employing the same pentaerythritol ester containing0.025 mol of 2,2-dipyridylamine to which was added varying proportionsof copper octoate. Table 2 which follows shows the data obtained in thisrespect and indicates that the optimum oxidation inhibition is obtainedwith molar ratios of free amine to copper between about 2 and about 75.The data given in the middle column of this table reflects the totalamine versus copper salt. Since the copper takes up two rnols of amineper mole of copper salt, the free amine is the net of the total amineminus 2.

The pentaerythritol ester base fluid was modified with 0.025 mol ofbenzoguanamine per liter of solution. The table which follows shows theeffect upon oxidation inhibition of adding copper octoate to thiscomposition. Copper octoate added in this manner forms a complex with apart of the amine in situ.

TABLE 3 Copper Molar ratio octoate in total OT, hours p.p.m. Cu+Amine/Cu EXAMPLE V Oil properties of oxidized oil.'1"'able 4 whichfollows shows the benefits gained by the use of a combination ofbenzoguanamine (BG) with varying amounts of copper catalyst. It isnoteworthy that within the claimed molar ratio the acid number of theoxidized oil is at a minimum, thus indicating that the peroxideproduction was also minimized by this combination.

TABLE 4 Amine 0.025 M Metal Molar ratio, OT, Acid N o.

amine/copper hours *Added as copper octoate.

EXAMPLE VI TABLE 5 (OT-14) N0. Additive, 0.025 M OT, 0T-14 l Combhours 1None 14 2 Benzoguanamine 15 3 4,4-n1ethylenebis (2,4-ditert butylphenol)27 Cu ootoate, 5O p.p.n1. Cu+ '16 (2)+(4) 62 +45 (3)+(4) 24 10 5 2)+3)+(4) 91 77 +61 EXAMPLE VII Preparation of oxidized 2,2-dipyridylamineand its copper complex.To 10 g. of 2,2-dipridylamine in a 100 ml.round-bottom flask was added 15 ml. glacial acetic acid. The solutionwas heated for 1 hour at 190 C. mantle temperature. After cooling toroom temperature, 20 ml. of 30 percent hydrogen peroxide was added andthe liquid temperature raised to C. for 1 hour and 80 C. for 2 hours. Anadditional 5 ml. of 30 percent hydroperoxide were added and thetemperature raised to .C. for 1 hour. To half of this solution was added3.4 g. of copper acetate monohydrate and the solution boiled to asemisolid. This was stored in a vacuum desiccator for 4 days withDrierite and sodium hydroxide pellets. 7

The above material was separated into 4 fractions by solvent extraction.The first portion was insoluble in ethanol, M.P. 400 C. Dilution of thealcohol solution with water gave a water insoluble second fraction, M.P.132-135 C. The third portion was a precipitate obtained by adding etherto an ethanol solution of fraction 2, M.P. 18l-l92 C. The filtnate offraction 3 gave fraction 4 on evaporation of solvent; it was a darkgreen viscous liquid and was ether, water and ethanol soluble.

The analysis of each fraction and effect on oxidation follow:

Fraction y Percent N Percent Cu N/Cu mol OT, hours ratio We claim as ourinvention:

1. A synthetic ester base lubricant composition comprising a majorproportion of a pentaerythritol tetraester of a fatty acid and minoroxidation-inhibiting proportions each of benzoguanamine and a copperoctoate complex with benzoguanamine, the mol ratio of total amine tocopper being between about 5 and about 35.

2. A synthetic ester base lubricant composition comprising a majorproportion of a pentaerythritol tetraester of a fatty acid and minoroxidation-inhibiting proportions each of 2,2-dipyridylamine and a copperdiacet-ate complex with 2,2'-dipyridylamine, the mol ratio of totalamine to copper being between about 5 and about 35.

3. A synthetic ester base lubricant composition comprising a majorproportion of a pentaerythritol tetraester of a fatty acid and minoroxidation-inhibiting proportions each of an aryldiaminotriazine and acopper complex of a copper C 24 fatty acid salt with a triazine, the molratio of total amine to copper being between about 5 and about 35. Y

4. A synthetic ester base lubricant composition comprising .a majorproportion of a pentaerythritol tetraester of a fatty acid and minoroxidation-inhibiting proportions each of 2,2'-dipyridylamine and acopper dioctoate complex with 2,2'-dipyridylamine, the mol ratio oftotal amine to copper being between about 5 and about 35.

5. A synthetic ester base lubricant composition comprising a majorproportion of a pentaerythritol tetraes-ter of a fatty acid and minoroxidation-inhibiting proportions each of 2,2'-dipyridylamine and acopper C -24 fatty acid salt complex with 2,2'-dipyridylamine, the molratio of total amine to copper being between about 5 and about 35.

6. A synthetic ester base lubricant composition comprising a majorproportion of a pen-taerythritol ester of an aliphatic monocarboxylicacid and minor oxidationinhibiting amounts each of diaminotriazine and acopper C 24 fatty acid salt complex with a pyridylamine, the mol ratioof total amine to copper being between about 2 and about 75.

7. A synthetic ester base lubricant composition comprising a majorproportion of a pentaerythritol ester and minor oxidation-inhibitingamounts each of a triazine and a copper C 24 fatty :acid salt complex,with a pyridylamine, the mol ratio of total amine to copper beingbetween about 2 and about 75. V

8. A synthetic ester base lubricant composition comprising a majorproportion of a pentaerythritol ester and minor oxidation-inhibitingamounts each of a pyridylamine and a copper C 24 fatty acid salt complexwith a pyridylamine, the mol ratio of 'total amine to copper beingbetween about 2 and about 75.

9. A synthetic ester base lubricant composition comprising (a majorproportion of a pentaerythritol ester of an aliphatic monocarboxylicacid and minor oxidationinhibiting amounts each of a dipyridylamine anda copper of the same group, the mol ratio of total amine to cop- 10 perbeing between about 2 and about 75.

1 19 References Cited in the file of this patent UNITED STATES PATENTS2,961,406 McNeil Nov. 22, 1960 2,962,439 Lauer Nov. 29, 1960 2,976,238Elliot et a1. Mar. 21, 1961 OTHER REFERENCES Atkins et al.: I. and E.Chem., vol. 39, No. 4, April 1957, pp. 491-493.

Barnes at 211.: Lubrication Engineering, August 1957, pp. 454-458.

10. A SYNTHETIC ESTER BASE LUBRICANT COMPOSITION COMPRISING A MAJORPROPORTION OF AN ALIPHATIC ESTER OF AN ALIPHATIC CARBOXYLIC ACID ANDMINOR OXIDATION-INHIBITING AMOUNTS EACH OF A COPPER C2-24 FATTY ACIDSALT COMPLEX OF AN AMINE OF THE GROUP CONSISTING OF PYRIDYLAMINES,AMINOTRIAZINES AND MIXTURES THEREOF AND A FREE AMINE OF THE SAME GROUP,THE MOL RATIO OF TOTAL AMINE TO COPPER BEING BETWEEN ABOUT 2 AND ABOUT75.